In a combustor of a gas turbine or the like, a premix type combustion method has been widely used. The premix type combustion method premixes fuel with compressed air (combustion air) fed from a compressor to generate mixed gas and causes the fuel-air mixture to be combusted (for example, see Patent Documents 1 to 3).
As this kind of combustor, there is known a combustor that has a pilot burner provided on the axis line of the combustor and a plurality of premixing burners disposed in parallel to the pilot burner. Further, the pilot burner and the premixing burner are fixed to the main body of the combustor by being supported by a substrate, on which support holes are formed corresponding to the radii of the pilot burner and the premixing burner. Further, the substrate is provided with a swirler cylinder, which has an elliptic cylindrical shape and is disposed so as to cover a premixing nozzle from the outside in the radial direction.
A premixing burner with such a configuration generates premixed gas by mixing fuel and air in the interior thereof, and forms a flame extending downstream from the tip of the swirler cylinder by combusting the premixed gas.
Here, in a gas turbine combustor employing the premix type combustion method, there is a possibility of stagnation occurring in the flow of the combustion gas in the region between a neighboring plurality of swirler cylinders. When stagnation of combustion gas occurs in such a region, an offset occurs in the concentration distribution of the combustion gas within the combustion cylinder. This leads to a decrease in combustion efficiency and an increase in nitrogen oxide (NOx) in the exhaust gas.
For example, patent document 1 describes a known technique for avoiding occurrences of such stagnation. In patent document 1, a combustor is described which is provided with stagnation eliminating structures which fill the space between swirler cylinders. These stagnation eliminating structures are substantially triangular pillar-shaped members formed so the width becomes smaller from the substrate toward the downstream side. These stagnation eliminating structures make it difficult for stagnation to occur from the combustion gas flowing out from the swirler cylinders by filling the spaces between swirler cylinders.
These stagnation eliminating structures are close to the flame because they correspond to the premixed gas channel outlets; in particular, the downstream end part of the stagnation eliminating structures is the part closest to the flame. Because of this, when stagnation of gas between swirler cylinders or the like occurs, there is a risk of a flashback phenomenon occurring. If a flashback phenomenon occurs, there is a risk of burning a premixing nozzle or a swirler cylinder.
Regarding burns occurring at the end part on the downstream side in this manner, the same patent document 1 proposes providing a plurality of hollow holes on the stagnation eliminating structures. This plurality of hollow holes is provided from the upstream side to the downstream side of the stagnation eliminating structures. The upstream side of the hollow holes is open, and the downstream side is closed. When a burn occurs from exposure to the flame, the closure on the downstream side opens up, air from the upstream side opening is supplied to the burned part, which mitigates further burns.